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SunnyDays

ERA5 almanac — 8 years of real data

Santorini in September

Santorini in September: 2% of days see measurable rain, 81°F average high, 86% of days historically clear (n=240, ERA5 2018–2025).

Historically one of the better months to visit Santorini for sun: 86% of days are clear on average (n=240, avg high 81°F). Every percentage here is a historical average from 8 years of ERA5 data — not a forecast.

What you are reading: 8-year historical averages from the ERA5 reanalysis, not a forecast. A month that is historically 90% clear can still be overcast on your specific trip. For this week’s actual forecast, see the live Santorini page. Both can be true at once: “historically strong in this month; this particular week is not.” We label which is which.

Early vs. Late September

Clear-sky percentage for Santorini in September, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period % Clear days Sample (n) Avg high
Early September
1st–15th		 87% n=120 81°F
Late September
16th–end		 86% n=120 81°F
Full month average 86% n=240 81°F

Sunshine & warmth in September

A second measure using actual sunshine hours (ERA5 sunshine_duration), not the daily weather code. A Lowcountry day with 12 hours of sun and a 25-minute afternoon storm is counted below as a warm, sunny day — because it was. How we define this.

Sunshine-based metrics for Santorini in September. Primary: % of days ≥ 72°F with > 6 h of sunshine.
Period Warm & sunny (≥72°F, >6 h sun) Sample (n)
Early September
1st–15th		 100% n=120
Late September
16th–end		 99% n=120
Full month average 100% n=240
11.9 h median sunshine per day 99% of days exceed 8 h sunshine 2% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 86%. Sunshine-based “warm & sunny”: 100%. The 14-point gap is from brief afternoon convective storms that stamp the whole day as “rain” in the WMO code but leave the bulk of the sunshine untouched.

Bottom line

Santorini is historically one of the best destinations for sun in September: 86% of days meet the clear bar (avg high 81°F, n=240 days across 8 years). Pack for outdoor activity — this month consistently delivers.

Every month in Santorini

Compare across all months with data. Numbers are historical clear-sky %.

Historical clear-sky % for Santorini, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 0% n=248 All destinations →
February 0% n=226 All destinations →
March 2% n=248 All destinations →
April 14% n=240 All destinations →
May 52% n=248 All destinations →
June 89% n=240 All destinations →
July 95% n=248 All destinations →
August 93% n=248 All destinations →
September ← this page 86% n=240 All destinations →
October 59% n=248 All destinations →
November 16% n=240 All destinations →
December 0% n=248 All destinations →

Frequently asked

Does it rain in Santorini in September?

Rarely. Only 2% of days in Santorini see measurable rain in September, based on 8 years of ERA5 historical data (n=240 days, 2018–2025). This is a historical average, not a forecast.

Is Santorini good for sun in September?

Yes. Santorini is historically strong for sun in September: 86% of days are clear on average (avg high 81°F, n=240 days, ERA5 2018–2025).

How Santorini compares in September

Head-to-head clear-sky comparisons against destinations travelers plausibly weigh against Santorini this month — same passport tier, similar flight distance, both sides from the same 8-year ERA5 record.

All percentages are historical averages from the ERA5 reanalysis via Open-Meteo, 8 full years (2018–2025). “Clear” means avg high ≥ 72 °F, precipitation < 1 mm, and a non-precipitation weather code. This is history, not a forecast. The live 7-day outlook for any destination is on its own page and may differ from the long-run average. Data from Open-Meteo.